1. Field of the Invention
The present invention relates to a light module, and more particularly to a light module, in which light sources are provided on upper and lower surfaces of a single printed circuit board.
2. Description of the Prior Art
In recent years, dual face flat panel displays have developed quickly and have been applied in electronic products such as mobile phones. Generally, the conventional dual face flat panel display uses only one light source for two display panels. Therefore, the light source cannot be effectively utilized. The brightness (luminance) is unstable, that is, the brightness of one face is lower, and the brightness of the other face cannot achieve the best result.
In order to improve the above disadvantage, some researchers use two light sources to supply two display panels. FIG. 1 is a cross-section of a conventional dual-faced LCD, which includes upper and lower LCD panels 100a and 100b, and a light module M interposed between the two LCD panels. The light module M includes two printed circuit boards 200a and 200b, two sets of light sources 300a and 300b, two light guiding plates 400a and 400b, reflector sheets 500 and 520, and two sets of optical sheets 600a and 600b. The optical sheet 600a includes one diffuser sheet 620a and two prism sheets 640a and 660a. The same, the optical sheet 600b includes one diffuser sheet 620b and two prism sheets 640b and 660b. 
Still referring to FIG. 1, the dual-faced flat panel display uses two printed circuit boards and a light source is provided on each printed circuit board. Specifically, the light source 300a is disposed on the printed circuit board 200a, and the light source 300b is disposed on the printed circuit board 200b. The light emitted from the light source 300a passes the light guiding plate 400a, the reflector sheet 500, the optical sheet 600a, enters the LCD panel 100a, and reaches face A. The light emitted from the light source 300b passes the light guiding plate 400b, the reflector sheet 500, the optical sheet 600b, enters the LCD panel 100b, and reaches face B.
The above structure has the following disadvantages:                (1) Face B has a much lower brightness than face A and it is difficult to control the stability standard of brightness.        (2) The light source cannot be effectively utilized and the brightness of face A cannot achieve the best result.        (3) The flat panel display with high brightness on both faces cannot be produced.        (4) The size along the y-axis direction is larger.        (5) Since the two light sources are disposed on two printed circuit boards respectively, two power supplies are needed. Thus, the structure is complicated and is not easy to assemble.        